The present invention relates to a printer for printing an image on a recording form by means of a so-called electrophotographic process.
A conventionally known electrophotographic imaging process is employed in a copying machine and so on, wherein the uniformly charged surface of a photoconductive drum is exposed to light which is reflected by or projected through an original image, to form a latent image thereon, toner is then adhered to the latent image to develop a visible image, and the developed toner image is transferred onto a recording form and fixed thereto by a fixing member.
Recently, a laser printer has been developed for printing an image on a recording form by means of an electrophotographic process wherein the circumferential surface of the photoconductive drum is scanned by a laser beam carrying optical image information, page by page, to form a corresponding latent image thereon.
In this laser beam printer, so-called cut-sheet recording forms which are cut into predetermined-size pieces are usually employed, and a so-called heat-fixing-roller pair is used to fix the toner image transferred onto the recording form. The heat-fixing-roller pair comprises a heat roller heated to a high temperature and a backup roller pressed against the heat roller, between which the cut-sheet recording form carrying a toner image passes so that the toner image is fused onto the recording form.
The above laser printer can of course be employed as a data output device of a computer, for which however it is preferable to use a continuous recording form as being done in a conventional line printer. The continuous recording form being generally used in the line printer is a so-called fan-fold sheet provided with a plurality of laterally arranged perforations where it can be folded and/or severed page by page.
For using this continuous recording form in the above laser printer, it becomes necessary to arrange a distance between an image-transfer point and an image-fixing point in the laser printer to substantially equal to the interval between the perforations of the continuous recording form, in order to prevent that transportation of the continuous recording form carrying the toner image from being stopped with remaining unfixed toner image portion between the heat-fixing-roller pair.
That is, since the image-printed continuous form is usually severed into pages after being discharged from the printer, the image must not be printed around the respective perforations. So, by arranging the distance between the image-transfer point and the image-fixing point to be substantially equal to the interval of the perforations, and by operating to stop the transportation of the continuous form at the time when the transferring of the toner image for the last page is completed, the vicinity of the respective perforations where no image is printed is placed at the image-fixing point, which prevents the above defect.
However, in case arranging as above, the printer becomes large-sized as a whole to ensure the necessary distance between the image-transfer point and the image-fixing point. Further, the printer as above arranged cannot employ various continuous recording forms with different perforation-intervals.